1. Field of the Invention
The present invention relates to technology of power amplification, and more particularly to a power amplifier with an automatic switching function, which is capable of variably controlling output power of circuits of the power amplifier, so that the circuits are fully operated when relatively large power is needed, and the circuits can be partially turned off when relatively small power is needed, according to magnitude of an envelope signal, such that the circuits can smoothly and automatically perform switching operations to improve efficiency and operation range thereof.
2. Description of the Related Art
A power amplifier used in a wireless mobile communication device has employed a method for controlling circuits thereof, such that the circuits can be partially operated to improve efficiency of the power amplifier in the entire operation range of output power. More specifically, the method increases efficiency of the power amplifier in the entire range of output power as all of the circuits are turned on when relatively large output power is needed and a part of the circuits is turned off when relatively small output power is needed.
Such a method has been disclosed in a report “Hyun-Min PARK, et al., ‘Demonstration of on-chip appended power amplifier for improved efficiency at low power region’ IEEE MTT-S International Microwave Symposium.”
FIG. 1 is a circuit block diagram illustrating a prior art power amplifier with a polar structure, which is used in a wireless mobile communication system.
As shown in the figure, a radio frequency input signal is a signal whose amplitude is constant and whose phase has information.
Generally, the envelope signal is a signal whose envelope has information in a voltage form, and whose frequency is less than that of a radio frequency signal.
When such an envelope signal is inputted to the power amplifier, the power amplifier can be switched.
Most of the power amplifiers are configured such that each power amplifier includes a plurality of amplification groups to guarantee satisfactory operation throughout entire range of the power amplifier and to improve efficiency of the power amplifier. More specifically, all of the amplification groups in the power amplifier are turned on when relatively large output power of the power amplifier is needed, and a part of the amplification groups is turned off when relatively small output power of the power amplifier is needed.
Therefore, a system employing such a power amplifier can improve efficiency thereof when small output power is needed.
Especially, a power amplifier with a polar structure, which is used in a wireless mobile communication system, can improve operation range thereof as a part of the amplification groups is turned off as occasion demands.
FIG. 2 is a circuit block diagram illustrating the prior art power amplifier whose amplification groups are three.
As shown in the figure, when the power amplifier is constructed to include a plurality of amplification groups, the plurality of amplification groups must be partially turned off according to change of magnitude of an envelope signal or change of output power. In order to determine as to whether the plurality of amplification groups are turned on or off, control signals 201, 202 and 203 are additionally applied to the amplification groups from the outside.
However, the prior art power amplifier employing the above-mentioned control method has disadvantages in that such additional control signals, which partially turn on/off the amplification groups, must be obtained from the outside. Also, the prior art power amplifier has drawbacks in that it complicates an external control circuit for generating the control signals.
Namely, the prior art power amplifier has disadvantages in that it requires external control signals from the outside, in which the control signals are applied to the power amplifier to partially turned off a part of the circuits in the power amplifier when magnitude of the output power is decreased to a predetermined level.
On the other hand, the prior art power amplifier has disadvantages in that, when a part of the circuits in the power amplifier is instantaneously turned off or on by the external control signals, characteristics of the circuits are abruptly changed such that the system using the power amplifier can be malfunctioned.